Health and usage monitoring systems (HUMS) are a common component in the flight deck avionics of a modern aircraft. The parameters that may be monitored by health and usage monitoring systems are extensive and may depend to some degree upon the configuration of the aircraft.
Among other functions, HUMS typically perform engine and drive train vibration monitoring, in order to detect mechanical faults and avoid mechanical failures. The HUMS typically consists of a variety of onboard sensors, algorithms, and data acquisition systems. For example, the following parameters may be monitored by HUMS. Speed probes and tachometer generators: the measurement of speed is of importance to ensure that a rotating component does not exceed limits with the risk of being overstressed. Temperature measurement: exceeding temperature limits or a tendency to run hot is often a prelude to a major component or system failure. Pressure measurement: a tendency to over-pressure or low pressure may be an indication of impending failure or a loss of vital system fluids. Acceleration: higher acceleration readings than normal may indicate that a component has been overstressed or that abnormal wear is occurring. The use of low-cycle fatigue algorithms may indicate blade fatigue, which could result in blade failure. Particle detection: metal particle detection may indicate higher than normal metal composition in an engine or gearbox oil system resulting from abnormal or excessive wear of a bearing which could fail if left unchecked.
Most HUMS systems when integrated with the flight deck avionics of a helicopter continuously monitor and log the above-mentioned parameters and would indicate to the pilot, via cockpit displays, when they have been exceeded. Even when the aircraft cockpit displays show normal, the data accumulated is regularly downloaded from the aircraft using a data transfer unit. The data may then be transferred to a ground-based computer and replay facility which performs the necessary data reduction and performance/trend algorithms, as well as providing a means of displaying the data. In this way it is possible to maintain a record of every aircraft and health and usage monitoring systems wherever installed in the fleet and to take the necessary actions when any unhealthy trends have been identified.
The level of HUMS functionality has led to increased safety that could be further improved by adding the capability of structural usage monitoring. Consequently, a comprehensive knowledge of actual aircraft usage would help assure safe operational procedures and usage profiles